Radiant heat drying method and apparatus



R. R. GOINS RADIANT HEAT DRYING METHOD AND APPARATUS 2 Sheets-Sheet 1 0 mm mm m 0m INVENTOR. R. R. GOI NS ATTORNEYS Nov. 23, 1965 Filed April- 9, 1962 Nov. 23, 1965 R. R. GOINS 3,219,329

RADIANT HEAT DRYING METHOD AND APPARATUS Filed April 9, 1962 2 Sheets-Sheet 2 INVENTOR.

R. R. GOINS ATTOR/VE United States Patent 3,219,329 RADIANT HEAT DRYING METHOD AND APPARATUS Robert R. Goins, Bartlesville, 0kla., assignor to Phillips Petroleum Company, a corporation of Delaware Filed Apr. 9, 1962, Ser. No. 186,014 13 Claims. (Cl. 26333) This invention relates to drying particulate material. In one aspect the invention relates to apparatus and a process for drying particulate material by passing the material through a drying zone in an agitated bed and heating by subjecting to radiant heat from a radiant burner. In another aspect the invention relates to a process and apparatus for drying particulate material in a rotary drum by subjecting the agitated bed of material in the drum to radiant heat from radiant burners. In another aspect the invention relates to a process and apparatus for chemical treatment of carbon black While subjecting it to radiant heat.

Frequently, in the production of particulate material, it is necessary to remove excess moisture from the material at some stage in the processing. Various types of dryers have been used to dry such products. In the processing of wet carbon black pellets, for example, rotary drum dryers have been widely and successfully utilized. However, sometimes it is desirabe to increase the rate of drying beyond the capacity of presently available dryers.

An object of this invention is to remove volatile liquid from particulate material. Another object of the invention is to increase the capacity of a rotary drum dryer. Another object of the invention is to dry wet carbon black pellets efficiently and rapidly. Another object of the invention is to provide accurately controlled, efficient, and rapid drying of particuate material. Another object of the invention is to chemically treat carbon black with oxygen at elevated temperature.

Other aspects, objects and the advantages of my invention are apparent in the written description, the drawing and the claims.

According to my invention there is provided a process for drying particulate material which comprises passing the material through a drying zone in an agitated bed while subjecting it to the heat from radiant burners.

Further according to my invention, there is provided a process for operating a rotary dryer by passing particulate material to be dried through the dryer While maintaining the material in an agitated bed by rotation of the dryer and subjecting the material to heat from radiant burners. Preferably the temperature of the bed is measured and controlled by controlling the flow of combustible mixture to the radiant burner. Separate control of the individual burners is provided by individually measuring the temperatures of the bed in the various locations influenced by the heat from each individual burner and controlling the flow of combustible mixture to that burner responsive to the particular temperature in its area of influence.

The process of my invention is particularly applicable to the drying of ammonium nitrate prills and wet pelleted carbon black pellets.

Further according to my invention, there is provided a dryer for particulate material comprising a rotary drum, means to rotate the drum at a controlled speed, means to move the particulate material through the drum while maintaining the material in an agitated bed, a radiant heater comprising a burner and means to impinge the flame from the burner on a refractory mass. Preferably means are provided to determine the temperature of the bed and to regulate the flow of combustible mixture to the burner responsive to this temperature. In one embodiment a plurality of individually controlled heaters 3,219,329 Patented Nov. 23, 1965 are provided and means provided to measure the temperature of the bed under the influence of each of the individual heaters and to control each heater separately. To permit the use of external radiation pyrometers, Windows are provided which close automatically in the lower portion of the drum where the particulate material is in contact with the wall of the drum and which are opened automatically in the upper portion to permit a direct line of sight from the pyrometers to the bed.

Further according to my invention, there are provided method and apparatus for chemical treatment of carbon black at elevated temperatures by the application of radiant heat.

In the drawing FIGURE 1 is an elevation, partly in cross section and partly schematic, of a rotary dryer utilizing automatic control.

FIGURE 2 is a cross-section along the line 2-2 of FIGURE 1.

FIGURE 3 is a diagram of apparatus used in a test of my invention.

In the drawing the dryer drum 11 is rotatably supported on rollers 12 and 13. In the embodiment illustrated, the rollers 13 are driven by an electric motor 14 and the speed of rotation of drum 11 is controlled by the speed of motor 14. Of course, other suitable driving means can be provided such as an internal combustion engine, and the drive from the prime move can be directed through gears, belts, chains, etc., as desired or necessary to provide the required speed of rotation and torque.

Drum 11 is provided with central, axial, openings in each circular end. The material to be dried is fed through one of these openings through feed pipe 16 from the source of moist particulate material, for example, a carbon black wet pelletizer (not shown). At the other end, withdrawal means are provided such as for example, collector 17. The entire drum 11 is tilted in the direction of flow, from left to right in FIGURE 1, to induce flow of the particulate material therethrough. The depth of the bed within the drum 11 is controlled by the means for discharging the material at the discharge end, usually an annular dam or dipping means, either of which regulates the height of the bed.

A support 21 is mounted outside drum 11 and extends through the drum, through the open ends thereof, to support the radiant burners and necessary feed pipes, etc., within the drum. A plurality of burners are provided, four burners 22, 23, 24, 25, being illustrated. A header 27 supplies a combustible mixture, such as, for example, a mixture of air and natural gas, to individual supply lines for each burner, lines 28, 29, 30, 31, 32- and 33, through which the'fiows are controlled by motor valves 36, 37, 38, 39, 40, and 41, respectively. Radiation pyrometers 46, 47, 48, 49, 50 and 51 are positioned above drum 11 as shown and each pyrometer is connected with a corresponding transducer-recorder-controller 54, 55, 56, 57, 58 and 59. The control output of these instruments is contacted to the corresponding motor valves 36, 37, 38, 39, 40 and 41.

A row of windows is provided around the periphery of drum 11 at locations opposite each of the radiation pyrometers. These windows provide openings permitting the corresponding pyrometers to receive radiation from the bed of particulate material and also, in some instances, are useful to permit combustion gases and vaporous moisture to be vented. Alternatively, a collector hood can be provided over the radiant burners, the hood being provided with windows opposite the pyrometers, the hood further being vented through one end of the drum and preferably being maintained under a slight vacuum to facilitate removal of the gases and the vapors. If desired, the pyrometers can be supported within dryer 11 by means of support 21 and the control leads extended through one end of the drum. Other temperature detecting means can be utilized, for example, thermocouples supported by support 21 and extending into the bed of particulate material, thermocouples extending through the outer shell of drum 11, etc. In the latter instance means are provided to connect only the thermocouples in contact with the bed at a given instant to indicate bed temperature.

In operation, drum 11 is made to rotate at a desired controlled rotational speed by energizing motor 14 to drive rollers 13. Particulate material to be dried enters through feed pipe 16 and drops into a bed within drum 11. As drum 11 rotates, the bed is maintained somewhat to one side, as seen more clearly in FIGURE 2, and is agitated by the rotation of drum 11, the particles on the surface of the bed being continually turned under and other particles exposed. Radiant burners, represented by burners 22, 23, 24, 25, are located at each of a plurality of heating zones spaced longitudinally along drum 11. Considering the operation of burner 22 for example, radiation pyrometer 47 senses the temperature of the bed directly under burner 22, transmits the signal to transducerrecorder-controller 55 which converts the temperature indication into a control signal, for example, air or electrical, which is transmitted to motor valve 37 to regulate the flow of combustible mixture to burner 22. The operation continues with the particulate material gradually traversing the length of dryer 11, and each of the burners in turn being controlled to maintain the desired temperature for that particular heating zone, the set point being adjusted in controllers 54, 55, 56, 57, 58 and 59 for the desired temperature at that location.

As seen more clearly in FIGURE 2, preferably the radiant burners are ofiiset from the vertical to direct radiant energy directly to the bed which is ofi'set as explained above due to the rotation of drum 11. Each of the windows 61 is provided with a hinge support 62, and each of the windows is made to close a corresponding opening in the shell of drum 11, indicated by the numeral 63 of FIGURE 1. With the direction of rotation of drum 11 as illustrated in FIGURE 2, it is noted that as each window passes along the left hand side of the drum as viewed in FIGURE 2, when the center of gravity of the window passes to the right of the corresponding hinge support 62 the window suddenly opens due to the force of gravity acting thereon. Each window remains open, being substantially fully opened as it passes by the corresponding radiation pyrometer, until that particular winto the force of gravity, closes, so that the window is closed at the time that portion of the drum shell passes under the bed of the particulate material being dried therein. The windows thereby provide the necessary opening for the operation of the radiation pyrometers but prevent loss of the particulate material from the bottom of the drum. In some instances a larger or smaller number of windows than the number illustrated can be used.

EXAMPLE In a test of my invention, the apparatus of FIGURE 3 was employed. The apparatus included a drum 66, 23 inches in diameter and 35 inches long and having internal longitudinal baffles /8 inch high, spaced at intervals. Wet pelleted carbon black was fed from a hopper 67, through a vibrating feeder 68, and an inlet pipe 69. Heat was supplied from radiant burner bank 70, comprising two type IR infrared burners, made by the Pyronics, Inc., Cleveland, Ohio, fed a combustible mixture of air and natural gas comprising substantially no excess oxygen. The effective radiating surface of the lower bank was 8 by 18 inches and was spaced 3 inches from the inlet end of drum 66. Thermocouples were positioned at 71, 72, 7 3, 74, and to measure the temperature within the bed of carbon black pellets at intervals of 1 inch, 4 inches, 12 inches, 20 inches, and 28 inches from the inlet end of drum 66. The drum was rotated at a speed such that the lineal peripheral speed of the drum shell was 63 feet per minute. Operating conditions and results obtained are in Table I below:

Oven Dried-Contr01 Maximum Temp. 300.

To determine whether there were adverse efiects on the dried carbon black pellets by exposure to the high temperature radiant burner, samples of the dried black were tested both for measurable characteristics of the black itself and for characteristics of rubber reinforced with the am les. Th r ul s f th s ar iven dow passes along the right hand edge of the section of 3 e as t 0 6 t6 ts e g m Table H FIGURE 2 at which time it is seen the window, again due T able II Sample NO 1 2 3 4 5 IRB#1 IRB#1 IRB#1 N Surface Area 119 115 117 Oil Absorption. 1. 07 1. 05 1. 05 1. 06 pH 8. 3 7. 0 7. 8 7. 7 Pack Point. 76 94 66 80 Modulus, p.s

15 mlnutes cure l, 520 1, 580 1, 670/1, 530 1, 550 1, 530 1, 840 1, 780 1, 850 30 minutes cure 1, 000 1, 990 2, 050/2, 050 1, 900 1, 900 2, 2, 150 2, Tensile, p.s.i.:

15 minutes cure 3, 200 3, 200 3, 550/3, 600 3, 550 3, 130 3, 420 3, 470 3, 600 30 minutes cure 3, 850 3, 670/3, 630 3, 750 3, 470 3, 720 3, 700 3, 700 Elongation, percent:

15 minutes eure- 500 500/530 520 500 480 490 480 30 minutes cure 490 470/470 500 460 470 450 470 Shore A Hardness:

15 minutes cure 59 59 60/58 59 60 60 59 57 30 minutes cure 62 62 62/62 63 64 62 62 62 Pellet Distribution (percent) on each screen Screen Mesh:

*, ***Use to show which samples were tested at the same time.

All runs were made with the same rubber formula and with the same cure. The asterisks designate runs made at the same time, all runs marked being made at one time, those marked at another, and those marked at still another time. IRB#1 refers to Industry Reference Black No. 1, an HAF black, a batch of which has been set aside for use throughout the industry for comparative purposes.

These data indicate the carbon black was not seriously affected by the drying, even when severely overtreated, as in Samples 1 and 3.

To determine the danger due to fire within the drum, the feed was stopped and the black in the drum circulated with the burner at 1550 F. After about 15 minutes the temperature of the black leveled off at 1200 F.; the burner was left on for 15 minutes more. Rotation of the drum was continued until the black cooled to 700 F. The black did not ignite under these test conditions.

In the drying tests, the percent of gross heat input from the gas combustion transferred to the carbon black by radiation was 31.2 percent; overall thermal efficiency was 38.4 percent. No attempt was made to recover heat in the exhaust gas.

Suitable radiant burners for use in my invention include, for example, burners comprising a ceramic cup and a burner which impinges a flame on the cup thus causing the ceramic material to glow and transmit radiant energy and burners having a block of porous ceramic material on which combustion takes place to cause incandescence of the ceramic mass. Either type of burner can be supplied with a metal screen or grid in front of the ceramic mass to cause a substantial amount of the radiant heat to be propagated from the metal surface. In this application, the word refractory has been used in its broad sense to include materials which are difficult to fuse or melt, and thus includes refractory metals and metallic compositions and cermet as well as ceramic materials. Cermet is used to mean a fired mixture of ceramic material and finely divided metal.

To prevent fluctuation in the signals received by radiation pyrometers 4651 and therefore a variation in the signals transmitted to the respective controllers and motor valves, a data converter such as the converter described in the ISA Journal, October 1958, pp. 28-31 can be inserted between each of the pyrometers and the corresponding controller. This has the effect of holding each temperature reading until the next reading is received. The gating of the converter can be accomplished by mechanical means as for example from the drive for drying drum 11 or from some part of drum 11 or can be by electrical means triggered by the temperature signals.

When my invention is used for drying ammonium nitrate prills the temperature is maintained within the range of 120 to 170 F., preferably in the range of 148 to 157 F. When my invention is utilized in drying wet carbon black pellets each of the heating zones is controlled to maintain a temperature in the range of 200 to 1000 F., that is each zone is controlled to a selected temperature within this range. Ordinarily, the maximum temperature of carbon black being dried is no higher than 500 F., preferably about 350 F.

The control of the temperature of ammonium nitrate prills while drying is to prevent crystalline phase changes. To prevent overheating the surface it is important that the prills be in a thin layer or in constant motion to expose different surfaces and different prills to the heat source. This is accomplished advantageously in a tumbling type dryer such as a rotary dryer as disclosed herein.

It is also important at the low drying temperature to provide a low humidity atmosphere to remove the expelled water. Thus in effect, the best dryer combines the use of radiant heat to heat the water internally within the prills, with the low humidity atmosphere of a convective 6 dryer. To maintain a low humidity it is desirable to remove the products of combustion.

As pointed out earlier, radiant heat is generated by a burning gas either by impinging a pre-existing flame on a mass of refractory material, or by causing combustion to occur on the surface of the refractory. In either case, a refractory mass is heated by burning a combustible gas. The gas can be premixed with air or other preoxygen containing gas, or can contact it at the instant of combustion.

Although all of the radiation pyrometers in FIGURE 1 are adapted to read the temperature of the bed of material being dried, one or more can be directed to measure the temperature of the drum. This may be particularly desirable near the inlet end of the drum where the material being dried is apt to contain excess moisture and thus be protected from overheating by the evaporating moisture, in which case excessive heating of the shell is a more likely contingency. Other means than radiation pyrometers can be used for temperature measurement, for example, thermocouples. Radiant burners operate well near stoichiometric air gas ratios with substantially no free oxygen.

Although my invention has been disclosed and is especially well suited for the drying of carbon black and ammonium nitrate, other materials such as urea, synthetic rubber, synthetic resins, etc. can be dried in this manner.

My invention is applicable to the chemical treatment of carbon block. This treatment can be carried out, for example by subjecting the black to a temperature in the range of 400 to 1000 F., preferably from 650 to 850 F., supplied by radiant energy in an oxidizing atmosphere in which the partial pressure of oxygen is in the range of 8 to mm. Hg. For the practice of my invention the temperature of the gas phase can be much lower than the required oxidation temperature which is maintained at the surface of the carbon black particles, thus minimizing heat loss in the off gas, resulting in improved thermal efficiency. The agitation can be provided by means of a vibrating conveyor or by means of a rotating drum or other means for maintaining a relatively thin agitated bed. The radiant burners utilized to supply heat to the carbon black can be controlled to maintain the desirable oxygen content in the combustion gases, preferably in the range from 0 to 10 percent or higher. The temperature within the treating zone can be maintained by controlling the fuel supply responsive to temperature measurements made on the surface of the carbon black bed, for example by radiation pyrometers. The oxygen content can be controlled by analyzing the off gas for oxygen or CO (for indirect control of oxygen) and automatically or manually adjusting the air supply to the burner.

Where drying and treating both are necessary they can be combined in a single treating unit or drying can be done in one bed and treating in another. Where drying and treating are carried out in a single vessel, the fuel-air ratio of separate burners can be separately controlled and the direction of the off gas movement regulated to maintain the desired oxygen content in the drying and treating portions of the zone.

My invention also is applicable to chemical treatment with other materials, for example, treatment with oxyhalides as disclosed in US. 2,641,533 (1953), S0 as disclosed in US. 2,636,831 (1953), etc.

Although when free oxygen is desired in the treating gas it can be obtained by operating the burners with an excess of air to produce combustion products having a desired amount of oxygen, it is also within the scope of my invention to vent all or part of the combustion products and to add treating gases containing the desired components, including oxygen if so desired.

When it is desired to prevent contact of the combustion products with the treated material, the combustion gas can be purged by the desired treating gas which flows over the carbon black.

Reasonable variation and modification are possible Within the scope of my invention which sets forth method and apparatus for drying particulate solid material by heating an agitated bed of the material with direct radiation from radiant burners, more especially an improved rotary dryer and the method of operation thereof, utilizing radiant heat from radiant burners Within the drying zone, and the application of the process and apparatus to the treating of carbon black at elevated temperature.

I claim: 1. A process for removing volatile fluid from partic ulate material, comprising:

passing said particulate material through a drying zone; maintaining said particulate material in an agitated bed in said drying zone; generating radiant heat by heating a refractory to incandescence in said zone by burning combustible gas; and heating said particulate material to remove said volatile liquid by subjecting said bed to said radiant heat. 2. A process for operating a rotary dryer having a rotating drum, comprising:

passing particulate material containing volatile liquid through said drum; maintaining said particulate material in an agitated bed by rotation of said drum; generating radiant heat by burning a combustible mixture and impinging the resulting flame on a mass of refractory material in said drum to cause said refractory material to glow; and heating said particulate material to remove volatile liquid by subjecting said bed to said radiant heat. 3. A process for removing volatile liquid from particulate material, comprising:

passing said particulate material through a drying zone; maintaining said particulate material in an agitated bed in said drying zone; generating radiant heat by heating a refractory to incandescence in said zone by burning combustible heating said particulate material to remove said volatile liquid by subjecting said bed to said radiant heat; measuring the temperature of said bed; and controlling the flow of said combustible gas to maintain said temperature. 4. A process for operating a rotary dryer having a rotating drum, comprising:

passing particulate material containing volatile liquid through said drum; maintaining said particulate material in an agitated bed by rotation of said drum; generating radiant heat in a plurality of heating zones spaced longitudinally in said drum by heating a refractory to incandescence in each of said heating zones by burning combustible gas; measuring the temperature of said bed in each of said heating zones; and controlling the flow of said combustible gas to each of said heating zones responsive to the measured temperature in each corresponding heating zone to maintain each of said temperatures. 5. A process for operating a rotary dryer having a rotating drum, comprising:

passing ammonium nitrate prills containing water through said drum;

maintaining said prills in an agitated bed by rotation and controlling the flow of said combustible mixture to each of said heating zones responsive to the measured temperature in each corresponding heating zone to maintain each of said temperatures in the range of 148157 F. 6. A process for operating a rotary dryer having a rotating drum, comprising:

passing Wet carbon black pellets through said drum; maintaining said pellets in an agitated bed by rotation of said drum; generating radiant heat in a plurality of heating zones spaced longitudinally in said drum by burning a combustible mixture and impinging the resulting flame on a mass of refractory material in each of said heating zones to cause said material to glow; measuring the temperature of said bed in each of said heating zones; and controlling the floW of said combustible mixture to each of said heating zones responsive to the measured temperature in each corresponding heating zone to maintain each of said temperatures in the range of 200-1000" F. 7. A dryer for removing volatile liquid from particulate material, comprising:

a rotary drum; means to rotate said drum at a controlled speed; means to feed said particulate material into and move said material through said drum to maintain said material in an agitated bed; means to generate radiant heat in said drum comprising a refractory mass, and means to heat said mass to incandescence by burning a combustible gas; and means to support said refractory mass in said drum to direct radiant heat to said bed. 8. A dryer for removing volatile liquid from particulate material, comprising:

a rotary drum; means to rotate said drum at a controlled speed; means to feed said particulate material into and move said material through said drum to maintain said material in an agitated bed; means to generate radiant heat in said drum comprising a refractory mass, and means to heat said mass to incandescence by burning a combustible gas; means to support said refractory mass in said drum to direct radiant heat to said bed; means to measure the temperature of said bed; and means to control the flow of combustible mixture to said burner to maintain said temperature. 9. A dryer for removing volatile liquid from particulate material, comprising:

a rotary drum; means to rotate said drum at acontrolled speed; means to feed said particulate material into and move said materials through said drum to maintain said material in an agitated bed; means to generate radiant heat in a plurality of heating zones spaced longitudinally in said drum comprising a refractory mass in each zone, and means to heat each of said masses to incandescence by burning a combustible gas; means to support each of said refractory masses in said drum in position to direct radiant heat to said bed; means to measure the temperature of said bed in each of said heating zones; and means to control the flow of combustible mixture to each of said burners responsive to the measured temperature in each corresponding heating zone to maintain each of said temperatures. 10. A dryer for removing volatile liquid from particulate material, comprising:

a rotary drum; means to rotate said drum at a controlled speed; means to f ed said particulatematerial into and move said particulate material through said drum at a rate to maintain said material in an agitated bed; means to generate radiant heat in said drum in a plurality of heating zones, comprising a refractory mass in each of said heating zones, and means to heat each of said masses to incandescence by burning a combustible gas; means to support each of said masses in said drum to direct radiant heat to said bed; a radiation pyrometer positioned outside said drum adjacent each of said zones; a plurality of openings around said drum at each of said zones; means to close each of said openings to prevent flow of said particulate material through said openings and open said openings to permit the corresponding radiation pyrometers to sense the temperature of said bed; and control means actuated by each of said radiation pyrometers to control the flow of combustible mixture to each said corresponding burner to regulate the temperatures in said bed in each of said heating zones. 11. A process for treating particulate carbon black which comprises:

contacting said carbon black with a free oxygen-containing gas in a treating zone; maintaining said particulate carbon black in an agitated bed in said treating zone; generating radiant heat by heating a refractory to incandescence in said treating zone by burning combustible gas; and heating said particulate carbon black to treating temperature by subjecting said bed to said radiant heat. 12. A process for chemical treating of particulate carbon black which comprises:

passing said particulate carbon through a treating zone; maintaining said particulate carbon black in an agitated bed in said treating zone; contacting said particulate carbon black in said treating zone with the desired chemical treating agent; generating radiant heat by heating a refractory to incandescence in said treating zone by burning combustible gas; and heating said particulate carbon black to treating temperature by subjecting said bed to said radiant heat. 13. A dryer for removing volatile liquid from particulate material, comprising:

a rotary dnum; means to rotate said drum at a controlled speed;

means to feed said particulate material into and move said particulate material through said drum at a rate to maintain said material in an agitated bed;

means to generate radiant heat in said drum in a plurality of heating zones, comprising a refractory mass in each of said heating zones, and means to heat each of said masses to incandescence by burning a combustible gas;

means to support each of said masses in said drum to direct radiant heat to said bed;

a radiation pyrometer positioned outside said drum adjacent each of said zones;

a plurality of openings around said drum at each of said zones;

a window for each of said openings;

means to attach each of said windows to said drum at a position adjacent a corresponding opening, said means to attach supporting said window in freely pivoting relationship with said drum, the pivoted axis being immediately behind the trailing edge of said opening in the direction of rotation of said drum to close each of said openings to prevent flow of said particulate material through said openings and to open said openings to permit the corresponding radiation pyrometer to sense the temperature of said bed; and

control means actuated by each of said radiation pyrometers to control the flow of combustible mixture to each said corresponding burner to regulate the temperatures in said bed in each of said heating zones.

References Cited by the Examiner UNITED STATES PATENTS 518,662 4/1894 Butterfield 263-33 X 1,415,990 5/1922 Carstens 263-32 X 1,841,625 1/1932 Musso 158-99 2,303,843 12/1942 Knoblauch 263-32 X 2,518,996 8/1950 Peckharn 236-15 2,642,273 6/1953 Dube 263-33 2,850,273 9/1958 Barnes 263-33 3,013,785 12/1961 King 263-33 CHARLES SUKALO, Primary Examiner.

JOHN J. CAMBY, Examiner. 

